In the near future, with further development and popularization of the mobile Internet, mobile data traffic will increase explosively. Global mobile data traffic is expected to increase by over 200 times from 2010 to 2020 and to increase by nearly 20,000 times from 2010 to 2030. In the future, a total quantity of devices connected to a global mobile communications network will reach hundreds of billions. A quantity of global mobile terminals (excluding Internet of Things devices) is expected to exceed 10 billion by 2020, and a quantity of global mobile terminals in China will exceed 2 billion. There will also be a rapid increase in a quantity of connected global Internet of Things devices, and the quantity of connected global Internet of Things devices will be nearly 100 billion by 2030, where a quantity of connected global Internet of Things devices in China will exceed 20 billion.
Currently, in a Long Term Evolution (LTE) system, uplink and downlink data scheduling is implemented by using a physical downlink control channel (PDCCH) or an enhanced physical downlink control channel (EPDCCH). In future communications, a very large quantity of connected users and a quantity of potential concurrently connected users present a challenge to a capacity of a control channel. A current LTE system is a scheduling-based uplink data transmission solution, but the capacity of the control channel is limited. When a quantity of concurrently connected users increases, a case in which a capacity of a data channel has a surplus but the capacity of the control channel is insufficient may occur, and in this case, the capacity of the control channel becomes a bottleneck of the system. Therefore, in a future evolved LTE system, optimizing overheads of the control channel will become an important tendency.
For example, one optimization tendency is that the scheduling-based uplink data transmission solution is evolved into a contention transmission-based uplink data transmission solution. In the solution, in a same contention transmission resource, a plurality of terminal devices for transmitting uplink data can directly send data without requiring uplink scheduling. A base station may distinguish data of different terminal devices by using demodulation reference signal (DMRS) sequences of the terminal devices, reducing scheduling overheads of a user. As shown in FIG. 1, time-frequency resources are classified into two types: a non-contention transmission resource and a contention transmission resource. A terminal device obtains the contention transmission resource by means of contention.
For a contention-based uplink transmission manner, when data needs to be sent, a terminal device contends for a time-frequency resource to send the data, and this is an initial transmission terminal device. If the initial transmission terminal device fails to transmit the data due to various reasons, and the base station feeds back a negative acknowledgement, the initial transmission terminal device applies for the time-frequency resource again for re-sending the data, and this is a retransmission terminal device. The contention-based uplink transmission manner can effectively alleviate a problem of the overheads of the control channel, but a retransmission conflict problem is introduced at the same time. For the retransmission terminal device, because the retransmission terminal device has experienced one failed initial transmission, the system should quickly make the retransmission terminal device successfully transmit the data as soon as possible. However, the retransmission terminal device may conflict with a potential initial transmission terminal device, and the conflict greatly reduces transmission reliability of a retransmission user in a contention transmission mode.
In conclusion, because of an inherent disadvantage of the contention-based uplink transmission manner in an existing wireless communications system, a novel data transmission method is urgently required in the art, so as to resolve a technical problem of transmission reliability in a case of proliferation of concurrently connected terminal devices.